Abstract: Physical Modeling of Salt Withdrawal and Dissolution Structures

Hongxing Ge, M. P. A. Jackson, B. C. Vendeville

Salt loss by withdrawal or dissolution is commonly regarded as causing crestal grabens above salt diapirs. In experiments, dry quartz sand modeled a roof of brittle sediments overlying a pre-existing diapir of viscous silicone. Deformation was induced by slowly withdrawing the silicone. Experimental diapirs had linear or circular planform, and various cross-sectional shapes (rectangular, semicircular, or triangular), with or without deposition during deformation.

Over a subsiding rectangular diapir, the roof formed a flat depression bounded by an inner zone of steep, convex-up reverse faults and an outer zone of late, normal faults. All faults merged at depth with the vertical diapir contact. Over diapirs initially having semicircular or triangular shape, the diapir roof inverted into a syncline, having a central contractional zone bounded by normal faults. Reverse faults propagated sequentially inward as salt welded out and overburden grounded onto the basement. Conversely, normal faults propagated outward, probably because of increasing topographic relief at the rim of the structure. Synkinematic sediment deposition retarded the growth of both normal and reverse faults, although the basic pattern of contractional and extensional faults remai ed similar. The fact that all experiments produced a complex association of reverse and normal faults indicates that simple crestal grabens above diapirs are not caused merely by salt withdrawal or dissolution. Rather, simple grabens are produced by regional extension or by arching above active diapirs.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994